Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $232.90   9.363%   $254.7064   $254.71   $254.70   $254.70  
  Purchase #2 $105.41   11.472%   $117.5026   $117.50   $117.50   $117.50  
  Purchase #3 $100.35   12.574%   $112.968   $112.97   $112.95   $113.00  
  Purchase #4 $119.58   7.361%   $128.3823   $128.38   $128.40   $128.40  
  Purchase #5 $54.31   12.335%   $61.0091   $61.01   $61.00   $61.00  
  Purchase #6 $179.99   8.121%   $194.607   $194.61   $194.60   $194.60  
  Purchase #7 $104.58   11.581%   $116.6914   $116.69   $116.70   $116.70  
  7 purchase totals = $897.12       $985.8668   $985.87   $985.85   $985.90